This invention relates to detecting units and in particular to remotely disposed detecting units for alarm systems.
A number of different detecting units responsive to pressure change, temperature change or presence of smoke for burglar alarm systems, fire alarm systems and smoke detecting alarms have been provided in the prior art for remotely controlling the actuation of an electrical device or alarm. Examples of U. S. patents illustrating such detecting units are those of:
U.S. Pat. No. 2,683,784, Rector, July 13, 1954
U.S. Pat. No. 3,125,739 Deibel et al., Mar. 17, 1964
U.S. Pat. No. 3,437,973, Mabbett, Apr. 8, 1969
U.S. Pat. No. 3,668,337, Sinclair, June 6, 1972.
Rector discloses a burglar alarm mat having a base member with a leaf spring supporting arm above the base member, a pair of contacts and a plunger to bring the contacts into engagement wherein the elongate, flexible supported arm actuates a trigger to release the plunger causing the contacts to engage, to thereby set off an alarm.
Deibel et al. discloses a contactor wherein a sheet of fibrous material separates a pair of conductive plates which operate to close a circuit through the fibrous material when the plates and fibrous material are compressed.
Mabbett discloses an electric switch comprising a matlike element having a first substrate member of interleafed fingers forming contact elements and a contact bridging element formed on the surface of a second substrate member. When pressure is applied to place the bridging element into contact with the interleafed fingers an electric circuit is completed.
Sinclair provides a matrix switch with orthogonally arranged flat conductor cables spaced apart by resilient elements of greater height than the height of the conductors so that when a force is applied to the upper set of conductors the switch is actuated into contact with the lower conductors at each intersection to complete a circuit.
A number of prior art systems utilize pre-formed mats with conducting elements arranged in matrix patterns actuated by pressure. A disadvantage of these systems resides in the limitation on their shape and extent. The conductors are fixed within a preformed geometric pattern which cannot conform to an area of any given geometric shape or size. Another disadvantage of the prior art systems is that they are limited in response to only a single form of physical change as, for example, pressure or if so desired a thermal change, but not both. The devices are not inherently fail safe. Electrical leads connecting them to the electric device to be operated are required and in the case of a burglar alarm, for example, these leads can be cut, disabling the alarm, or they can become inadvertently broken.
In burglar alarm systems it is desirable to cover as much open area as possible and to dispose the sensing elements in unpredictable patterns. It is also desirable to have high density detection nearer doors and windows and sensing means near cabinets which appear to contain valuables. It is also necessary in fire detection systems as well as in burglar alarm systems to have fail safe detection units which will energize the system when the wires are cut or inadvertently broken.